The present invention relates to tires comprising colored markings, in particular characters or logos or other symbols, on their surface.
It is nowadays desirable to be able to embellish tires with colored markings, preferably with several different colors, and it is particularly desirable to obtain perfect sharpness of molding because these markings are used for mainly aesthetic reasons. In order to obtain such markings, several techniques are known to the person skilled in the art, and in particular U.S. Pat. No. 3,769,123 describes a process for depositing colored rubber mixes during building on a tire blank. The uncured tire blank is then introduced into a tire mold in order to be molded and vulcanized. This process does not provide sufficient accuracy as to the position of the colored motifs and requires, for example, covering these colored mixes with a thin layer of black rubber to effect the molding and the vulcanization of the tire in its mold before taking up this tire again in order to remove this black rubber locally by grinding in order to make the subjacent color(s) of the colored motif appear, while having lines of transition between the different colors [with] the desired sharpness.
In order to reduce the number of operations and to obtain, directly after molding the tire, a colored motif which contrasts with the color of this tire, U.S. Pat. No. 4,684,431 discloses a process using a mold comprising a housing within which is placed an insert having appropriate magnetic properties to hold a metal support covered on one of its faces by a colored appliqué´of a non-vulcanized rubber mix. Then a tire blank is introduced into this mold in order to mold it, to vulcanize the mixes and to connect the colored appliqué´to said tire. During the molding of the tire, the appliqué´is integral with the tire with its support; then this metal support is removed by peeling.
In another process, described in U.S. Pat. No. 1,371,501, a mold is used which also comprises a housing intended to receive an insert in which there is formed a recessed motif which is filled with at least one non-vulcanized colored rubber mix such that, once the insert bearing the colored motif is in place in its housing, the continuity of the molding surface of the mold is produced both by the surface of the insert and by the surface of the colored motif before fitting in the tire blank.
Although they are of interest since the number of operations on the tire after curing is reduced, these latter two processes are not entirely satisfactory due to the fact that it has been noted that the limits of the colored motifs were not sufficiently sharp and precise and that an adverse change in the aesthetic appearance of the tire close to these motifs resulted. The Applicant has observed that this adverse change was amplified with the molding pressure used for molding the tire: in particular, the molding of a tire built on a rigid core results locally in very high pressures, which result in movements of the rubber mixes of different colors which become visible on the molded tire. It is thus very complicated to obtain colored markings forming a relief on the outer surface of the tire which have very sharp, precise contours.